The present invention relates to overvoltage and overcurrent protection apparatus for telecommunication circuitry and method of manufacturing same. In particular, the invention relates to fuses and thyristors.
Circuitry, particularly sensitive circuitry such as that found in telecommunication systems, require protection against both overcurrent and overvoltage conditions that may arise. Conditions such as short circuits may arise requiring an overcurrent protection device, such as a fuse, in order to prevent damage to circuitry.
Lightning is a common source of overvoltage in communication systems. Typically, communication systems consist of conductors in shielded cables suspended on poles or buried in the earth. The cable is made up of many conductors arranged in twisted pairs, commonly known as xe2x80x9cTipxe2x80x9d and xe2x80x9cRingxe2x80x9d lines for telephone systems, in particular. These cables are susceptible to transient energy from lightning and may conduct energy from the lightning to either a central office or subscriber equipment. Additionally, power sources for telecommunication systems are usually obtained from commercial power lines, which are also subject to excess energy from lightning that can, in turn, induce overvoltages in the telecommunication system being supplied by the power line.
Common approaches in the art to mitigate overcurrents and overvoltages include a combination of a fuse and a semiconductor overvoltage device such as a bi-directional thyristor, as shown in the circuit of FIG. 1. A fuse 100 is placed in series with a copper twisted pair 102 either in the Tip line 104 or in the Ring line 106. Hence, the fuse 100 protects the tip and ring wiring and also a bidirectional thyristor 110 from excessive energy in the event a continuous overvoltage is coupled to the wiring, as might occur if a power line falls across the wiring.
In order to limit overvoltage conditions, an overvoltage device such as the bi-directional thyristor 110 is connected across the twisted pair 102 in parallel with the telecommunication system 108. The thyristor 110 provides bidirectional xe2x80x9ccrow-barxe2x80x9d clamping of transients that may occur for either polarity. In particular, the thyristor 110 has a breakdown voltage at which a transient voltage exceeding this value will cause the thyristor 110 to begin clamping action across the lines 104 and 106. As the transient voltage attempts to rise higher, the current through the thyristor 110 will increase until a break-over voltage is reached. At this point, thyristor action is triggered and the thyristor 110 switches to its xe2x80x9conxe2x80x9d or xe2x80x9clatchedxe2x80x9d state. This is a very low impedance state that shunts or xe2x80x9ccrow-barsxe2x80x9d the line, thereby suppressing the magnitude of the transient voltage. When the transient voltage diminishes, the thyristor 110 turns off and reverts to a high impedance xe2x80x9coffxe2x80x9d state.
The circuit of FIG. 1 is commonly used to protect xe2x80x9cTipxe2x80x9d and xe2x80x9cRingxe2x80x9d connections such as modems, telephones, facsimile machines, and line cards. While the circuit of are also suitable for circuits sought to be protected such as alarm circuits, power supplies, remote sensors, CATV, data lines, etc.
The protection circuits used in telecommunication applications, such as that shown in FIG. 1, commonly utilize discretely packaged fuse and thyristor components connected in printed circuit wiring. The discrete component approach, however, requires that the components be properly coordinated and matched with one another in order to meet pertinent regulatory and safety agency requirements. Also, the discretely packaged components are typically sourced separately, thus adding increased cost to the final product. Furthermore, using discrete components consumes considerable physical space on a printed circuit since two separate component packages must be placed on the printed circuit.
There is a need for an improved circuit device that achieves both overcurrent and overvoltage protection in a discrete integral package to more easily assure coordination and matching of the overcurrent and overvoltage devices. In addition, there is a need for a discrete integral package approach that affords lower final product cost and reduces the physical space consumed in a printed circuit.
These and other advantages are provided by the present invention, where overcurrent and overvoltage protection devices are packaged in a common housing to form a single discrete circuit element that is substantially no larger than one of the overcurrent or overvoltage devices that are each discretely packaged as previously known in the art, such as a standard surface mount telecommunications fuse, for example.
In an embodiment, the present invention provides an integral circuit protection device providing overcurrent and overvoltage protection for a circuit that is configured to be connected to the circuit. The device includes an overcurrent protection portion, an overvoltage protection portion, and a plurality of terminals for connecting both the overvoltage and overcurrent protection portions of the integral circuit device to the circuit to be protected. Incorporation of both overvoltage and overcurrent devices into a single housing assures that these components are coordinated and matched for a particular application, lowers the total cost of the device since the components are not sourced separately and allows for smaller size by incorporating the devices into the same package.
In another embodiment the plurality of terminals includes first, second and third terminals with the overcurrent protection portion electrically connected between the first and second terminals and the overvoltage protection portion connected between the second and third terminals.
In another embodiment, the overcurrent protection portion includes a fuse.
In another embodiment, the overvoltage protection portion includes a bi-directional thyristor.
In another embodiment, the plurality of terminals of the integral circuit are configured to electrically connect the overcurrent protection portion in series with the circuit to be protected and to electrically connect the overvoltage protection portion in parallel with the circuit to be protected when the integral circuit device is electrically connected to the circuit to be protected.
In yet another embodiment, the integral circuit further includes a thermally conductive portion that conducts heat away from the overvoltage protection portion.
In an embodiment, thermal coefficients of the thermally conductive portion and overvoltage protection portion are substantially the same.
In an embodiment, the overvoltage protection portion is at least partially encapsulated with an atmospherically resistant material.
In another embodiment, the integral circuit device is configured for mounting on a printed circuit board.
In another embodiment, the integral circuit device is configured substantially the same as a standard telecommunications fuse configuration.
In yet another embodiment of the present invention, a circuit element is provided for overvoltage and overcurrent protection of a circuit. The circuit element includes a circuit element housing having first, second and third terminals. An overcurrent protection device is electrically connected between the first and second terminals and contained by the circuit element housing. In addition, an overvoltage protection device is electrically connected between the second and third terminals and also contained by the circuit element housing.
In an embodiment, the circuit element housing is comprised of a tube having an outer surface, an inner hollow portion, a first end and a second end. The overcurrent protection device is disposed within the inner hollow portion of the tube, the overvoltage protection device and the second terminal are disposed on the outer surface of the tube, the first terminal is disposed at the first end and the second terminal is disposed at the second end opposite from the first terminal.
In another embodiment, the first and second terminals include electrically conductive layers disposed on the outer surface of the tube adjacent to each of the first and second ends and extending into part of the inner hollow portion adjacent to the first and second ends. Additionally, conductive end caps respectively cover the electrically conductive layers and the first and second ends and are electrically connected to the electrically conductive layers.. The electrically conductive layers are also electrically connected to the overcurrent device disposed within the inner hollow portion of the tube.
In yet another embodiment, the third terminal is comprised of a conductive terminal disposed on the outer surface of the tube.
In another embodiment, a die bond pad is disposed on the outer surface of the tube. A bond pad conductor is also disposed on the outer surface of the tube and electrically connected to at least one of the first and second conductive layers. A first conductor electrically connects the bond pad conductor to the die bond pad and a second conductor electrically connects the third terminal to the die bond pad. A thyristor is disposed on the die bond pad and covered with an encapsulant material.
In an embodiment, the encapsulant material is atmospherically resistant and disposed such that the thyristor and the die bond pad on the outer surface of the tube are sealed to resist surrounding atmosphere.
In another embodiment, the thyristor disposed on the die bond pad is bonded to the die bond pad by a thermally conductive bonding material.
In an embodiment, the circuit element housing includes a substrate having first and second surfaces and a plurality of wire terminations disposed on at least one of the first and second surfaces, wherein the first, second and third terminals are each respectively comprised of one of the plurality of wire terminations.
In an embodiment, the overcurrent device is comprised of a fuse element electrically connected between the first and second terminals and disposed on at least one side of the substrate. The overvoltage device is comprised of a thyristor electrically connected between the second and third terminal and disposed on at least one side of the substrate.
In a further embodiment of the present invention, a circuit element is provided for overvoltage and overcurrent protection for circuitry in a telecommunications system. The circuit element includes a fuse element, a semiconductor overvoltage protection device, and a package configured as a discrete component that is mountable on a printed circuit board, the package containing the fuse element and the semiconductor overvoltage protection device.
In another embodiment, the package includes first, second and third terminals. In addition, the fuse element and the semiconductor overvoltage protection device both include corresponding first and second lead connections. The first terminal is connected to the first lead connection of the fuse element, the second terminal is connected to the second lead connection of the fuse element and the first lead connection of the semiconductor overvoltage protection device and the third terminal is connected to the second lead connection of the semiconductor overvoltage protection device.
In a still further embodiment of the present invention, the invention provides a method for providing an overcurrent and overvoltage device in a telecommunications circuit. The method includes providing a housing configured to receive an overcurrent protection element and an overvoltage protection element, the housing having a plurality of terminals. The overcurrent and overvoltage protection elements are disposed within the housing such that the overcurrent protection element is electrically connected between first and second terminals of the plurality of terminals and the overvoltage protection element is electrically connected between the second terminal and a third terminal of the plurality of terminals. Finally, the housing is connected as a single discrete element to a circuit board that includes the telecommunications circuit.
In an embodiment, the method includes electrically connecting one of the first and second terminals to a first incoming line to the telecommunications circuit and electrically connecting the other of the first and second terminals to the telecommunications circuit such that the overcurrent protection element is connected in series with the telecommunications circuit, and electrically connecting the third terminal to a second incoming line to the telecommunications circuit such that the overvoltage protection element is connected in parallel with the telecommunications circuit.
Additional advantages and features of the present invention will become apparent upon reading the following detailed description of the presently preferred embodiments and appended claims, and upon reference to the attached drawings.